The present invention relates to a ferroelectric liquid crystal composition and a liquid crystal display element employing the composition.
Practical liquid crystal display elements have chiefly employed nematic liquid crystals. These display elements have been applied to various kinds of display devices including watches, conventional electronic calculaters, and sophisticated display devices such as color televisions and other opto-electronic display devices. Although liquid crystal display devices have been developed, there has been unexpectedly limited scope for the application of these display elements because of their unsatisfactory electro-optic response. Various attempts and researches have been made to increase the response rate of the display device by means of improving liquid crystal materials, however, there is expected little room for improvement on the response properties by reducing viscosity of liquid crystal materials or by increasing dielectric anisotropy of the materials.
R. B. Meyer and others presented a liquid crystal display element having a large electro-optic response and employing a ferroelectric liquid crystal which has been very attractive. As a ferroelectric liquid crystal has spontaneous polarization (hereinafter abbreviated to Ps) liquid crystal molecules can easily be aligned under an electric field. Consequently, it becomes possible to drive the device at a large electro-optic response rate.
There still lie many problems to be solved before applying the ferroelectric liquid crystal to a practically usable display element. These problems include an inner structure of a liquid crystal cell, a method for aligning ferroelectric liquid crystals in a cell, a means to drive the liquid crystal element, and so forth. Streneous efforts have continuously been made by reseachers to solve those problems. Almost all of those researches have been carried out on a ferroelectric chiral smectic C phase (hereinafter abbreviated to SC* phase) and a surface stabilized ferroelectric liquid crystal mode (abbreviated to SSFLC mode). As the SSFLC mode makes use of bistable states of aligned molecules at SC* phase, the display device can exhibit only two domains which are bright and dark, respectively. In other words, it is difficult to exhibit gradation of image which is required in television display and the like. Thus, the application of the SSFLC mode at SC* phase is limited in scope considerably.
According to a twisted nematic mode (abbreviated to TN mode) at which the gradation of image is available, an electro-optic response is very small. Therefore, it may be present state of the art, heretofore, that there was no liquid crystal display having both a large electro-optic response and gradation of image together.